Torque limiting coupling

ABSTRACT

A torque limiting coupling having a driving member and a driven member and which limits the amount of torque transmitted between the members. When excessive torque is attempted to be transmitted, the coupling is released and over-runs freely until the coupling is reset by causing reversal of its relative direction of rotation. The coupling utilizes a plurality of balls which act between pockets in the two opposing members, thereby causing axial separation and release of the coupling when one of the members rotationally moves relative to the other.

United States Patent Steinhagen 51 Mar. 27, 1973 [54] TORQUE LIMITINGCOUPLING Primary Examiner-Allan D. l-lerrmann [75 1 Inventor. Horst G.Stemhagen, Racine, Wis. Atmmey JameS E Nines 73 Assi nee: Twin DiscIncor rated Racine, 1 g p0 57 ABSTRACT [2'2] Filed: Jam 31, 1972 Atorque limiting coupling having a driving member and a driven member andwhich limits the amount of PP 221,935 torque transmitted between themembers. When excessive torque is attempted to be transmitted, the [52]192/56R 64/29 coupling is released and over-runs freely until the [51]Intel i F16; 43/20 coupling is reset by causing reversal of its relative[58] new 64/29 direction of rotation. The coupling utilizes a pluralityof balls which act between pockets in the two opposing members, therebycausing axial separation and [56] References Cited release of thecoupling when one of the members rota- U ED STATES PATENTS tionallymoves relative to the other.

3,080,029 311963 Stober ..64/29 X R 8 Claims, 22 Drawing Figures3,305,058 2Il967 Orwin et al. .....64/29 X R 3,429,407 2/1969 Orwin etal. ..64/29 X R TORQUE LIMITING COUPLING BACKGROUND OF THE INVENTION Theinvention pertains to torque limiting couplings such as overloadclutches having driving and driven clutch members connected together bytorque transmitting balls and which engage in torque transmittingpockets in axially opposed faces of the driving and driven members. Themembers are mounted for relative axial displacement away from oneanother against resilient means, such as a spring, which urges themembers towards one another.

An example of one type of prior art over-load clutch is shown in the US.Pat. No. 3,305,058 which issued Feb. 21, 1967 to Orwin et al. and isentitled Overload Clutch. This and many other types of torque limitingclutches have been used with a reasonable degree of success.

One of the problems however in the prior art devices was the difficultyencountered in attempting to reset the coupling after it had beenreleased. Such resetting often necessitated the use of tools to urge theballs to their previous position in their respective driving slots andit was difficult to force the balls into alignment with their ramps andcages. Furthermore, when a device such as shown in the US Pat. No.3,305,058 was released, the balls continued to roll around and did notprovide complete release of the unit without some drag effect.Additionally, many of the prior art devices were incapable of beingreset from any point in the power drive line and could not be resetautomatically.

SUMMARY OF THE PRESENT INVENTION The present invention provides a torquelimiting coupling which is capable of functioning in either direction ofrotation. After the coupling has been disengaged due to excessivetorque, it overruns freely and can run in the disengaged condition forextended periods of time without damage.

In addition, the coupling provided by the present invention can be resetsimply by reversing the relative direction of rotation of the drive anddriven members. Because of this ability to be reset by simply reversingdirection of rotation, such resetting can be accomplished from any pointin the power drive line.

The coupling provided by the present invention is completely sealedagainst foreign matter and need not be opened to be reset. The amount oftorque required for release is accurately maintained and is notappreciably affected by rotational speed or vibration. Furthermore, theamount of torque required for release can be easily adjusted.

These and other objects and advantages of the present invention willappear hereinafter as this disclosure progresses, reference being had tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal, crosssectional view through a torque limiting coupling embodying the presentinvention;

FIG. 2 is a transverse sectional view taken along line 22 in FIG. 1 andshowing the ball engaging surface of the driven member;

FIG. 3 is a transverse, cross sectional view taken along line 3-3 inFIG. 1 and showing the ball cage;

FIG. 4 is a transverse, cross sectional view taken along line 4-4 inFIG. 1 and showing the ball engaging surface of the driving member;

FIG. 5 is an enlarged, fragmentary cross sectional view, of a portion ofthe coupling shown in FIG. 1, but in a flat lay-out position, andshowing the position of one of the torque transmitting balls when it islocated in the driving pockets of the driving and driven members when intorque transmitting condition; 7

FIG. 6 is a cross sectional view taken along line 6-6 in FIG. 1 andunder the same operating conditions as in the FIG. 5 showing;

FIG. 7 is a view similar to FIG. 5, but showing the condition whenexcessive torque was applied and one of the members when it has rotatedrelative to the other so as to cause the balls to move out of theirdriving pockets so as to axially separate the driving and drivenmembers;

FIG. 8 is a view similar to FIG. 6, but showing the position of theparts when the FIG. 7 condition exists;

FIG. 9 is a view similar to FIGS. 5 and 7, but showing the coupling whenthe members have rotated relative to one another to a position in whichthe ball has been engaged in the reset pocket of the driving member;

FIG. 10 is a view similar to FIGS. 6 and 8, but when the members haverotated relative to one another as shown in FIG. 9, and wherein the keyfixed on the ball cage is holding an axially shiftable plate of thedriving member a spaced distance from a shoulder on the driving shaft;

FIG. 11 is a view similar to FIGS. 5, 7 and 9, but showing the memberswhen the coupling is overrunning and a pocket of the driven membermatches up with a reset pocket of the driving member and the springpushes the ball out of the reset pocket.

FIG. 12 is a schematic view of the ball when located in the positionshown in FIG. 11 and showing the force vector which acts on the ball;

FIG. 13 is a view similar to FIG. 11, but showing the direction ofrotation of the members reversed from the FIG. 1 1.

FIG. 14 is a view similar to FIG. 13, but showing the position of theball when it has been moved out of the reset pocket, thereby forcing thedriving and driven members to axially separate;

FIG. 15 is a view similar to FIG. 14 and showing the coupling in thereset position after which it can be driven in either direction;

FIG. 16 is a fragmentary, perspective view of the key on the ball cage;

FIG. 17 is a view similar to FIG. 4, but showing a modification of thedriving plate which utilizes uneven spacing of the pockets whereby themembers can be in driving position for only one relative circumferentialrelationship to one another;

FIG. 18 is a view similar to FIG. 2 but showing the pocket spacing ofthe driven member when used with the FIG. 17 modification;

FIG. 19 is a view similar to FIG. 3 but showing the pocket spacing ofthe cage when used with the FIG. 17 modification;

FIGS. 20-22 show a modification of the invention;

FIG. 20 is a view similar to a corresponding portion shown in FIG. 1;

FIG. 21 is a view of a reset pocket in member 10 of FIG. 20; and

FIG. 22 is a cross sectional view taken along line 2222 in FIG. 20, butlaid out in a flat position.

DESCRIPTION OF A PREFERRED EMBODIMENT A torque limiting coupling hasbeen shown in FIG. 1 for the purpose of illustrating the presentinvention and includes a driving member in the form of a driving shaft 1which receives its power from a power shaft (not shown) connected bymeans of the tapered collet 3 located within and cooperating with thetaper 4 of the driving member 1. The collet is adjustable in the usualmanner by the screw 5 so as to form a driving engagement between thedriving member 1 and its power source (not shown). The driving shaft 1has an external spline 6 around its periphery and to which is splined adrum 7. The drum in turn has a series of internal teeth 8 on the innersurface of its axially extending flange 9 and a driving plate 10 hasexternal teeth 12 by means of which it is in constant mesh with theteeth 8. Thus, the input driving shaft 1, the drum 7, and the axiallyshiftable plate 10 all rotate together as the driving member.

A plurality of springs 13 are located in circumferentially spacedpockets 14 in the drum 7 and bear against the plate 10 and resilientlyload it to the left as viewed in FIG. 1. The resilient load of thesprings 13 can be adjusted by means of the adjusting nut 15 that isthreadably engaged on the end of the shaft 1.

The plate 10, as shown in FIG. 4, has a series of circumferentiallyspaced driving pockets 10a formed in its transverse surface 11 andevenly spaced from one another. The plate 10 also has a series of evenlyspaced reset pockets 10b, some of which have a spring 100 therein.

The driven member of the coupling includes an annular ring having anexternal peripheral surface 22 that is located within the flange 9, anda seal 23 is located between the surface 22 and the inner surface of theflange 9 so as to completely seal the coupling.

The driven ring 20 has a transverse surface 21 that opposes surface 11of the plate 10. As shown in FIG. 2, a series of drive pockets 20a areformed in evenly, circumferentially spaced locations in the surface 21of ring 20.

The driven member also includes a tapered hub portion 24 which isrigidly fixed to the ring 20 by means of the cap screws 25. The drivenmember in general is journalled by means of the anti-friction needlebearing assemblies 26 and the anti-friction ball bearing assemblies 27which are located on the periphery of the driving shaft 1.

Means are provided on the driven member so as to transmit powertherefrom, and this means has been shown as a sheave 28 which is fixedto the hub 24 for rotation therewith. Other transmitting means may beused such as sprockets, gears, pulleys, or other members, andfurthermore, other forms of driving and driven members may be employed.

Torque transmitting and torque limiting means are provided between thedriving plate 10 and the driven ring 20 and this means includes a seriesof hardened steel balls 30 which are adapted to ride against thesurfaces 11 and 21 of members 10 and 20 and also drop into the drivingpockets 10a and the reset pockets 10b of plate 10 and the drive pockets20a of ring 20. A ball cage 33 has a plurality of generally elongatedopenings 34 circumferentially spaced therearound, as shown in FIG. 3.The cage 33 also has three circumferentially spaced key-ways 35 in whichare fixed the keys 36 so that they extend from either side of the cage.A pin 37 (FIG. 1) extends through each of the three keys 36 and into aperipheral groove 37 of shaft 1 to hold the cage axially fixed on theshaft. The cage assures that the balls all move simultaneously and actsto support the balls against centrifugal forces and this feature rendersthe torque setting of the coupling independent of rotational speed.Furthermore, the pockets 34 in the cage 33 can be shaped in such amanner that the radially outer support of the balls is not located onthe centerline of the balls, but rather in a direction towards the ring20. Such a disposition of the cage relative to the balls would cause theballs to be urged towards the reset springs 10c when centrifugal forceacts on the balls. This would permit the ring 20 to rotate completelyfreely above a predetermined rotational speed.

FIGS. 5 to 15 show the various positions of the driving member 10 andthe driven member 20 relative to one another under certain operatingconditions.

In FIG. 5, the balls 30 are shown as being located in the drive pockets10a and 20a of members 10 and 20, respectively. This is the normaltorque transmitting, driving relationship between the parts. In thisposition, torque may be transmitted in either direction of rotation ofthe coupling.

The transmittable torque is a function of the ball ramp angle a (alpha),ball pitch radius, and the force produced by the springs 13.

When the applied torque exceeds the predetermined amount of torque setin the coupling, the balls 30 begin to roll out of the pocket 10a and20a and the members 10 and 20 are thus forced apart as shown in FIG. 7against the compression of springs 13. As shown in FIG. 6, when theparts are in the driving relationship shown in FIG. 5, the key 36 whichis rigidly attached to the cage 33 is located within one of the radiallyextending openings like in the plate 10. The other end of the key 36 isabutting against a shoulder in of the shaft 1. In this position, the key36 is ineffective.

Referring to FIG. 8 which is the position of the plate 10 relative tothe shoulder la when the coupling is in the position shown in FIG. 7,here it will be noted that the key 36 has been withdrawn from theopening 10a of plate 10. It will be noted that the length of the key 36is less than the space between the plate 10 and shoulder la of the shaftwhen the coupling is in the position shown in FIG. 8.

As the plate 10 and ring 20 rotate relative to one another further asshown in FIG. 9, the balls 30 drop only partially into the reset pockets10b of the plate 10 which also contain the light reset springs 100. Inother words, it is only necessary for the balls 30 to move into thepockets a small distance in order for the keys 36 to become effective.The reset torque would become too high if the balls roll too deep intothe reset pockets. In any event, this movement of the balls into thepockets slightly, causes the plate 10 to move towards the ring 20 due tothe action of the springs 13. This movement reduces the space betweenplate 10 and ring 20. As shown in FIG. 10 the key 36 has moved out ofthe recess We and because the space between the plate 10 and ring 20 isreduced, the key 36 then prevents any further reduction of the spacebetween plate and ring 20. In other words, the force of the springs 13is taken by the key 36 against the shoulder Ia of the shaft, and theballs 30 are thus unloaded except for the very small force of the resetsprings 100. Therefore, the ring 20 can rotate freely on its supportinganti-friction bearings. Cage 33 is prevented from further rotation dueto the frictional forces acting on the keys 36. To further preventrotation of the cage 33 beyond the desired position, another key 38 isfixed in a corresponding key-way 38a in plate 10. In other words, thekey 38 rests on the periphery of shaft 1 and is so positioned that it iscontacted by one of the keys 36 and thus provides a positive stop in arotational direction for the cage 33.

Upon further rotation of the members relative to one another from thatshown in FIG. 9, the balls 30 will be forced into the next succeedingpocket 20a by the light reset springs 10c as shown in FIG. 11. The faceedge 40 of the cage pockets prevent rotational movement of the balls 30.The forces acting on the balls in that position are shown in FIG. 12 andit will be noted that the pocket angle or ramp angle a (alpha) must beselected small enough to allow the balls 30 to slide axially againstface 40, compress springs 10c, and allow further rotation of the ring20.

In FIGS. 11 and 12 it will be noted that the space between surfaces 11and 21, in the released position, is just slightly less than the balldiameter.

To reset the coupling, the relative direction of rotation must bereversed and this action is shown in FIG. 13. Here again, as in FIG. 12,the balls are out of the reset pockets due to the spring force ofsprings 10c.

When the pockets 20a of ring 20 are in axial alignment with the balls30, the reset springs 10c will push the balls into the pockets 20a asshown in FIG. 13. The balls can move circumferentially because of theelongated openings 34 of the cage. In other words, as shown in FIG. 13,the space 41 in the openings 34 permit the ball to travel relative tothe cage.

Further rotation of the ring 20 relative to plate 10 will wedge theballs between the edge of the pockets 20a and 10b. Under theseconditions where the ball gets ahead of the pocket 10b, the balls cannotgo back into the pockets and therefore the plates must separate.

Further rotation of the ring 20 will force the plate 10 against thesprings 13, thus releasing the keys 36 and the cage 33. The clearancebetween the balls and the cage openings 34 must be large enough topermit the balls to return to this position, thereby releasing the cage,otherwise the friction resistance of the cage would force the balls backinto pockets 10b. Further rotation of the ring 20 relative to plate 10permits the balls to roll back into the drive pockets 10a of plate 10(FIG. 15) and finally also into successive pockets a of ring 20. FIG. 5is the final reset position and the coupling can then drive in eitherdirection after this resetting operation.

Referring to a modification of the pocket arrangement in the parts, asshown in FIGS. l7, l8 and 19, the spacing of the drive pockets 10a (FIG.17) and the resetting pockets 10b in the plate 10 are uneven. With thismodification of the uneven spacing of the pockets, because the pocketsare irregularly spaced, the pockets between the plate 10 and the drivenring 20 can be axially aligned for a driving connection only in onecircumferentially matched position. In other words, the parts must bearranged in one particular circumferential relative position to effect adriving engagement. Therefore, the resetting of the coupling in thismodification only occurs in one relative position between the parts.This is useful in certain applications where the alignment between thedriving and driven shafts must be made in only one position between theshafts and where simply providing matching marks between the shafts isnot sufficiently positive.

The embodiment shown in FIGS. 20, 21 and 22 is generally the same as tothe operation above described, but the plate I0 and ring 20' arefabricated from sheet steel. A belleville spring 50 is located on thestud bolts 51 and provides the resilient loading of the plate 10'towards the driven member 20'. The circumferentially spaced stud bolts51 support the spring 50, the driving member 10 and driven member 20'and also the ball cage 33'. Holes 33a in the cage provide a solid stopfor the cage on bolts 51. The driven member 20' has external teeth 52around its periphery which can be connected to a member (not shown).Anti-friction needle bearing assembly 53 is provided for journaling thedriven member 20 and is located between the member 20 and the plate 55which is secured on the bolts 51.

The power input can be to the driving member 10' either at the outeredge where power input attaching holes 56 are located or the inner edgewhere power input attaching holes 58 are located. The center line thatis the shaft on which the device is mounted, can be at either side asindicated by the center lines 60 or 61. Ramps 62 and 63 in plate 10' andcage 33 provide the same function as do the keys 36 in the FIG. 1device. Three sets of these ramps may be provided.

Depressions 64 in the cage may not be essential under all conditions,but they serve to increase the effective thickness of the cage.

The pocket spacings in members 10', 33' and 20' are the same as those inthe corresponding parts 10, 33 and 20 of the FIG. 1 4 device.

I claim:

1. A rotatable torque limiting coupling comprising, a driving memberhaving an axially shiftable plate, a driven member, said plate and saiddriven member having opposed transverse surfaces, said plate surfacehaving a plurality of circumferentially spaced drive pockets and resetpockets, said driven member surface having a plurality ofcircumferentially spaced drive pockets in radial alignment with thepockets of said plate, a plurality of balls located between and abuttingagainst said plate surface and said driven member surface and engagablein said pockets, a ball cage for holding said balls captive therein,spring means located in at least some of said reset pockets of saidplate, and resilient means urging said plate towards said driven membersurface, whereby when torque over a predetermined amount is applied tosaid coupling, said balls ride out of said drive pockets, therebyaxially separating said plate and driven member to cause disengagementof said coupling, and continued relative rotation between said plate anddriven member causes said balls to engage-in said reset pockets of saidplate, whereby when the relative direction of rotation between saidplate and driven member is reversed said spring means push said ballsout of said reset pockets and said balls again engage in said drivepockets.

2. The coupling set forth in claim 1 further characterized in that saidball cage has key means abuttable against said plate for holding thelatter separated from said driven member surface until said relativerotation is reversed.

3. The coupling as described in claim 2 further characterized in thatsaid plate has an opening in radial alignment with said key means forreceiving the latter when said key means is not holding said plateaxially separated from said driven member.

4. A torque limiting coupling comprising a generally cylindrical drivingmember having an axially extending annular flange, a shiftable platemounted in said flange and fixed thereto for rotation therewith andaxially movable relative thereto, a driven member journalled on saiddriving member and extending axially within said flange for sealingengagement therewith, said plate and said driven member having opposedtransverse surfaces, said plate surface having a plurality ofcircumferentially spaced drive pockets and also having a plurality ofcircumferentially spaced reset pockets, said driven member surfacehaving a plurality of circumferentially spaced drive pockets in radialalignment with the pockets of said plate, a plurality of balls locatedbetween said plate surface and said driven member surface and adapted toabut against said surfaces and engage in said pockets, a cage having aplurality of elongated openings for holding said balls captive therein,spring means located in at least some of said reset pockets of saidplate, and resilient means urging said plate towards said driven membersurface whereby when torque over a predetermined amount is applied tosaid coupling, said balls ride out of said drive pockets, therebyaxially separating said plate and driven member to cause disengagementof said coupling, and continued relative rotation between said plate anddriven member causes said balls to engage in said reset pockets of saidplate, whereby when the relative direction of rotation between saidplate and said driven member is reversed, said spring means push saidbails out of said reset pockets and said balls again engage in saiddrive pockets.

5. The coupling set forth in claim 4 further characterized in that saidball cage has key means abuttable against said plate for holding thelatter separated from said driven member surface until said relativerotation is reversed.

6. The coupling as described in claim 5 further characterized in thatsaid plate has an opening in radial alignment with said key means forreceiving the latter when said key means is not holding said plateaxially separated from said driven member.

'7. A torque limiting coupling comprising a driving member, said drivingmember having an axially shiftable plate, a driven member, said plateand said driven member having opposed transverse surfaces, said platesurface having a plurality of circumferentially spaced drive pockets andalso having a plurality of circumferentially spaced reset pockets, saiddriven member surface having a plurality of circumferentially spaceddrive pockets in radial alignment with the pockets of said plate, aplurality of balls located between said plate surface and said drivenmember surface and adapted to abut against said surfaces and engage insaid pockets, a

cage having a plurality of elongated openings for holding said ballscaptive therein and for limited circumferential travel of said balls insaid openings, spring means located in said reset pockets of said plate,and resilient means urging said plate towards said driven member surfacewhereby when torque over a predetermined amount is applied to saidcoupling, said balls ride out of said drive pockets, thereby axiallyseparating said plate and driven member to cause disengagement of saidcoupling, and continued relative rotation between said plate and drivenmember causes said balls to engage in said reset pockets of said plate,said cage having key means for holding said plate separated from saiddriven member surface until the relative direction of rotation betweensaid plate and said driven member is reversed whereby said spring meanspush said balls out of said reset pockets and said balls again engage insaid drive pockets, said plate having an opening in radial alignmentwith said key means for receiving the latter to permit axial movement ofsaid plate towards said driven member.

8. A coupling as defined in claim 1 further characterized in that saidplate and driven member are fabricated from sheet metal stampings.

* l i i

1. A rotatable torque limiting coupling comprising, a driving memberhAving an axially shiftable plate, a driven member, said plate and saiddriven member having opposed transverse surfaces, said plate surfacehaving a plurality of circumferentially spaced drive pockets and resetpockets, said driven member surface having a plurality ofcircumferentially spaced drive pockets in radial alignment with thepockets of said plate, a plurality of balls located between and abuttingagainst said plate surface and said driven member surface and engagablein said pockets, a ball cage for holding said balls captive therein,spring means located in at least some of said reset pockets of saidplate, and resilient means urging said plate towards said driven membersurface, whereby when torque over a predetermined amount is applied tosaid coupling, said balls ride out of said drive pockets, therebyaxially separating said plate and driven member to cause disengagementof said coupling, and continued relative rotation between said plate anddriven member causes said balls to engage in said reset pockets of saidplate, whereby when the relative direction of rotation between saidplate and driven member is reversed said spring means push said ballsout of said reset pockets and said balls again engage in said drivepockets.
 2. The coupling set forth in claim 1 further characterized inthat said ball cage has key means abuttable against said plate forholding the latter separated from said driven member surface until saidrelative rotation is reversed.
 3. The coupling as described in claim 2further characterized in that said plate has an opening in radialalignment with said key means for receiving the latter when said keymeans is not holding said plate axially separated from said drivenmember.
 4. A torque limiting coupling comprising a generally cylindricaldriving member having an axially extending annular flange, a shiftableplate mounted in said flange and fixed thereto for rotation therewithand axially movable relative thereto, a driven member journalled on saiddriving member and extending axially within said flange for sealingengagement therewith, said plate and said driven member having opposedtransverse surfaces, said plate surface having a plurality ofcircumferentially spaced drive pockets and also having a plurality ofcircumferentially spaced reset pockets, said driven member surfacehaving a plurality of circumferentially spaced drive pockets in radialalignment with the pockets of said plate, a plurality of balls locatedbetween said plate surface and said driven member surface and adapted toabut against said surfaces and engage in said pockets, a cage having aplurality of elongated openings for holding said balls captive therein,spring means located in at least some of said reset pockets of saidplate, and resilient means urging said plate towards said driven membersurface whereby when torque over a predetermined amount is applied tosaid coupling, said balls ride out of said drive pockets, therebyaxially separating said plate and driven member to cause disengagementof said coupling, and continued relative rotation between said plate anddriven member causes said balls to engage in said reset pockets of saidplate, whereby when the relative direction of rotation between saidplate and said driven member is reversed, said spring means push saidballs out of said reset pockets and said balls again engage in saiddrive pockets.
 5. The coupling set forth in claim 4 furthercharacterized in that said ball cage has key means abuttable againstsaid plate for holding the latter separated from said driven membersurface until said relative rotation is reversed.
 6. The coupling asdescribed in claim 5 further characterized in that said plate has anopening in radial alignment with said key means for receiving the latterwhen said key means is not holding said plate axially separated fromsaid driven member.
 7. A torque limiting coupling comprising a drivingmember, said driving member having an axially shiftable plate, a drivenmember, said plate and said driven member having opposed transversesurfaces, said plate surface having a plurality of circumferentiallyspaced drive pockets and also having a plurality of circumferentiallyspaced reset pockets, said driven member surface having a plurality ofcircumferentially spaced drive pockets in radial alignment with thepockets of said plate, a plurality of balls located between said platesurface and said driven member surface and adapted to abut against saidsurfaces and engage in said pockets, a cage having a plurality ofelongated openings for holding said balls captive therein and forlimited circumferential travel of said balls in said openings, springmeans located in said reset pockets of said plate, and resilient meansurging said plate towards said driven member surface whereby when torqueover a predetermined amount is applied to said coupling, said balls rideout of said drive pockets, thereby axially separating said plate anddriven member to cause disengagement of said coupling, and continuedrelative rotation between said plate and driven member causes said ballsto engage in said reset pockets of said plate, said cage having keymeans for holding said plate separated from said driven member surfaceuntil the relative direction of rotation between said plate and saiddriven member is reversed whereby said spring means push said balls outof said reset pockets and said balls again engage in said drive pockets,said plate having an opening in radial alignment with said key means forreceiving the latter to permit axial movement of said plate towards saiddriven member.
 8. A coupling as defined in claim 1 further characterizedin that said plate and driven member are fabricated from sheet metalstampings.